Use 'mildewed' when something is damaged by fungus, indicating it's usually damp and smelly. The old book had a mildewed cover due to humidity.
Pro Tip 2/3
Negative Sensation
'Mildewed' suggests a strong unpleasant smell and feel, which is important to express disgust or disapproval. She cringed at the mildewed scent in the air.
Pro Tip 3/3
Poor Condition
Describe objects in poor condition with 'mildewed' to emphasize neglect or decay. The mildewed curtains showed the room hadn't been used in years.